Post-Knox Ordovician stratigraphic sequences and the significance of the Rocklandian K-bentonites, eastern United States

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5808123

Haynes, J T ^[1]

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1. George Mason Univ., Fairfax, VA (United States). Dept. of Geography and Earth Science

The depositional sequences of the post-Knox Ordovician are reinterpreted and summarized, with emphasis on the stratigraphic importance of the Rocklandian K-bentonites relative to the various sequence-defining unconformities associated with them. The Deicke and Millbrig K-bentonite Beds can be traced through the subsurface to Cincinnati Arch exposures, where a remarkably similar stratigraphy occurs; fenestral micrites (Tyrone/Carters Fms.) unconformably underlie fossil-rich limestone (Lexington/Hermitage Fms.). The Deicke and Millbrig, however, both occur in the fenestral micrites below the unconformity, rather than above it, a stratigraphy which suggests that if this post-Tyrone unconformity is the same as the post-Quimbys Mill unconformity, it is a diachronous surface, climbing upsection and crossing the K-bentonites southeast of the Upper Mississippi Valley. In eastern belts two lesser unconformities are associated with the K-bentonites. Locally in Birmingham, AL, a post-Chickamauga unconformity is 4 m above the Millbrig and is overlain by a thin Sequatchie Fm., itself unconformably overlain by the Silurian Red Mountain Fm. In VA between Roanoke and Wytheville on the Pulaski and Cove Mountain thrust sheets, the Deicke is absent and a sub-Bays unconformity exists where the Walker Mountain Sandstone, a pebbly quartz arenite 18--28 m below the Millbrig, overlies Black River limestones. The post-Tyrone unconformity, like the older post-Knox unconformity, is a regionally extensive hiatus, suggestive of a eustatic sea-level change. By contrast, the unconformities that are restricted to only the eastern Valley and Ridge may be evidence of tectonism along the continental margin during the ordovician. Similarly localized unconformities are recognized in Silurian and Devonian strata as well throughout the southern Appalachians.

• OSTI ID: 5808123
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

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GEOLOGIC HISTORY
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